Electrical instrument



s Sheets-Sheet 1' Filed Jan. 14, 1933 R m m R m m 0 b MT -5 m I W %?0ATTORNEY Nov. 27, 1934. v. s. THOMANDER ELECTRICAL INSTRUMENT 3Sheets-Sheet 5 Filed Jan. 14, 1935 f e m Y R E mm m 0 W T m A 5 mm P h &E S S E N W W Patented Nov. 27, 1934 UNITED STATES;

PATENT OFFICE.

ELECTRICAL INSTRUMENT Pennsylvania Application January 14, 1933, SerialNo. 651,837

8 Claims.

My invention pertains to galvanometers and iarticularly to galvanometerssuitable for use with amplifiers as in cardiographs.

It is an object of my invention to provide a galvanometer of improvedsensitivity for cardiographs whereby one or more stages of amplificationmay be omitted or making possible a two stage amplifier for cardiographapplication.

It is also an object of my invention to provide a rugged compactgalvanometer of simple design.

vAnother object of my invention is to provide a galvanometer in whichthe mirror and magnet assembly may be conveniently adjusted to anangular position to allow for the normally large direct current outputof an amplifier.

A further object of my invention is to provide a galvanometer support inwhich a galvanometer may be conveniently assembled comprising an oiltight casing in which the galvanometer may be readily adjusted duringoperation.

The invention itself, however, both as to its organization and itsmethod of operation, together with additional objects and advantagesthereof, will best be understood from the following description of aspecific embodiment when read in connection with the accompanyingdrawings, in which Figure 1 is a view in front elevation showing agalvanometer completely assembled in accordance with my invention;

Fig. 2 is a sectional view thereof taken on line I[II of Fig. 1;

Fig. 3 is a plan view thereof;

Fig. 4 is a cross-sectional view on line IV--IV of Fig. 2;

Fig. 5 is a-detail view showing a front eleva tion of the vibratorassembly on an enlarged scale;

Fig. 6 is a side elevational view thereof partly in section;

Fig. 7 is an enlarged sectional view taken along the line VII-VII ofFig. 6, showing the angular relation of the indicating unit and itsvibrator ribbon with reference to the yoke member;

Fig. 8 is an enlarged side elevational view showing the indicator unitin side elevation;

Fig. 9 is a front elevational view thereof.

Fig. 10 is a sectional view taken along the line X-X of Fig. 8;

Fig. 11 is a rear sectional view of the magnetic structure taken on lineXI.XI of Fig. 12;

Fig. 12 is a side elevational view thereof;

Fig. 13 is a sectional view through the electromagnets in a plane at 90degrees to the section of Fig. 11; and

Fig. 14 is a diagrammatic view representing the circuit connections forenergizing the electromagnets.

Referring more specifically to Fig. 1 of the drawings, my galvanometercomprises a supporting housing 1 which is pivotally suspended on pivotpins 2 in an inverted U-bracket 2. The bracket is fastened to anysuitable instrument board 3 in any suitable manner as by screws 3'.

A knob 4 is disposed in front of the instrument board 3 for convenientlyadjusting the angular position of the galvanometer mirror duringoperation in a manner to be subsequently set forth.

Referring to Fig. 2, it will be seen that the housing is closed on oneside by a magnetic shield cover 5 and encloses a galvanometer casing 6which is secured to the bottom of the magnetic shield or housing 5 bysuitable screws 7. The galvanometer casing 6,-in turn, completelyencloses and supports the element of the galvanometer and is closed atthe back by a closure plate 8 secured in oil tight engagement with thecasing by suitable screws 9. y

The front wall of the galvanometer 6 is provided with an orifice toreceive a glass lens 12 which is held firmly seated by a threaded ring13. By placing suitable cement onthe lens and its retaining ring, priorto seating them, an oil tight joint is assured. Binding posts 14 aremounted in insulated relation in the front wall of the galvanometercasing 6 in any well known manner to afford connection with the interiorthereof. The cover 5 of the supporting housing 1 is provided with openportions through which the window and the binding posts are exposed.

The structure of the galvanometer, which is mounted within the casing 6,comprises a front plate 21 having a laterally projecting arm extendingfrom each edge and bent perpendicular thereto. The various perpendiculararms extending back from the front plate comprise a pair of side arms22, an upper arm 23 and a lower arm 24, as shown in Figs. 2, 4, 11 and12.

The magnetic circuit comprises a pair of pole pieces 26, and a U-shapedpiece 28 as a return circuit of extremely low-inductive magneticmaterial, which are secured between the two intermediate arms 22 in suchrelation that the pole tips are disposed in adjacent spaced relation toform an air gap 27. The curved U-shaped magnetic member 28, whichcarries magnetic fiux around the air gap 27 and back to the outer endsof the pole pieces 26, is securely fastened to the pole pieces 26 asclearly shown in Fig. 11. The outer end of eac le piece 26 is providedwith a head 29 which is clamped between one end of the U-shaped member28 and one of the side arms 22 by screws 30. The elements are therebysecured into a rigid compact assembly and the reluctance of the magneticcircuit is diminished.

The tips of the pole pieces 26 are preferably tapered, as clearly shownin Fig. 13, to provide a concentrated field in the air gap 27. In orderto still further concentrate the flux in the air gap, the magnetomotiveforce for energizing the magnetic circuit is provided by two windings34, one of which is disposed on each pole piece 26 adjacent to the poletip.

By placing the coils 34 on the pole tips, the magnetomotive force isapplied to a point in the magnetic circuit where the reluctance of themagnetic path is concentrated, and consequently, the magnetic fluxdensity in the air gap is greatly increased. This contributes toincrease the current sensitivity of the instrument. Another advantage ofhaving the coils so close together on opposite sides of the air gap isthat all the flux must pass between them and will not go out intosurrounding space and interfere with other galvanometer elements. Themagnetic circuit return to the coils is of low reluctance; therefore,little leakage will result.

The cross section of the pole pieces 26 is made small thereby reducingthe size and mean turn of the coil and its reactance and resistance fora given number of coil turns. The voltage-sensitivity of the instrumentis thus greatly increased. Conversely the small core makes it possibleto provide a coil of a greater number of turns, having the sameresistance and reactance and thus further increases the currentsensitivity of the galvanometer.

In assembling the instrument, the flat portion of the front plate 21 issecured to the front wall of the galvanometer casing 6 by suitablescrews 35. The plate 21 is provided with openings arranged to admit theterminal connectors 14 and the window 12.

The vibrator assembly, as clearly shown in Figs. 5 and 6, comprises ayoke 41 having bridges 42 thereon. A tensioning means is providedcomprising a lever 43 which is pivotally mounted on a screw 44. One endof the lever 43 is biased by' an adjustable tensioning spring 45 and theother end is secured to a vibrator ribbon 46 which passes over thebridges to an anchor 46' above the upper bridge. The spring ispreferably stretched to about forty grams tension.

Attached to the vibrator ribbon 46 is an indicator unit 47 comprising amirror 48 and a pair of small permanent magnets 49 of cobalt steel. Tosecure this unit to the ribbon, the permanent magnets 49 are cementedtogether with the ribbon 46 clamped between, and the mirror 48 iscemented to the edges of the magnets, as shown in Figs. 8, 9 and 10.

The surfaces of the bridges 42 are cut atan angle of about 45 degrees tothe plane of the yoke 41, and when the vibrator ribbon 46 is tensionedbetween the bridges, it supports the indicator unit 47 in an angularposition, as shown in Fig. 7. This allows a large deflection in onedirection for the normally large direct current output of the amplifieralso the bridges are cut at a 15 degree angle the other way, as shown atthe top of bridge 42, to make a knife edge on the inside edge ofeachbridge, to insure that the vibrator ribbon will always ride on these twoedges, and give a definite bridge spacing 42' of about one inch.

The ends of the yoke 41 are pivotally supported by pivot pins 52 and 53which extend through the extremities of the respective upper and lowerarms 23 and 24, respectively, projecting from the front plate 21. Theorifices for receiving the pivot pins are provided in the yokeextremities in exact axial alignment with the vibrator ribbon 46 and thelatter is so positioned that it extends through the air gap 27 andsupports the indicating unit 47 directly between the pole tips where'thedensity of the flux is greatest. A spring washer 54 under the head ofpivot pin 52 applies sufllcient tension. to hold the yoke 41 firmly inany adjusted position.

Since the rotation of the yoke 41 on its pivots is about an axis whichextends lengthwise through the ribbon, the angular position of the crosssection of the ribbon 46 and of the indicating unit 47 thereon will bevaried as the yoke is turned, but the axial alignment of the ribbon inthe air gap 27 will not be disturbed. This renders possible the use of asmall air gap, the dimensions of which are comparable with the magnetsof the indicating unit itself which are thereby exposed to the-maximumflux density available.

After the galvanometer is assembled and its casing has been filled withoil, the angular position of the vibrator yoke 41 may be convenientlyadjusted from the front of the instrument board by manipulating the knob4. The knob 4 rotates the yoke 41 through a suitable interconnectingmechanism comprising a dial shaft 61 which is journalled in a bearing 62supported by the U- bracket 2. The shaft and its bearing are elongatedand extend through an opening 63 in the instrument board 3 to supportthe knob 4 adjacent the front of the board. The outer end of the shaft61 is provided with a shoulder 64 which predetermines its position inthe bearing and the inner portion of the shaft carries a collar 65 whichabuts the inner end of the bearing and is rigidly secured to the shaft61 by a screw 66. A small pinion 67 is rigidly secured on the end of theshaft in any suitable manner, and operatively engages a gear wheel 68which is journalled on astud shaft 69 depending from the bracket 2.

The gear wheel 68 carries a pin 71 which projects into a slot in one endof a bifurcated lever 72. The opposite end of the lever 72 is providedwith a split bearing 73 and a screw 74 which clamps it onto the end of agalvanometer shaft 75 which extends into the galvanometer casing. Thegalvanometer shaft 75 is provided with a flanged shoulder 76 which isseated in a bearing in the upper end of the galvanometer casing. Theflanged shoulder 76 is secured in position by an end bearing plate 78and a screw 79 which is threadably received by the end wall of thecasing 6.

The bearinghas a long oil creepage surface and is provided with numerousglands 81 for the reception of a strong lye soap 82 which is therebyheld in compressed engagement with the shaft and its flanged shoulder.Such a bearing is completely oil proofand positively prevents thecreepage of oil out of the galvanometer casing along the shaft. When oilcomes in contact with the lye in the soap, more soap is made and theopening between the bearing and the shaft is closed. This bearing hascompletely eliminated difliculties caused by oil creepage.

The lower end of the galvanometer shaft 75 carries a lever arm 83clamped thereto in any suitable manner as by a split end 84 and screw85.

The free end of the lever 83 is bifurcated. A pin 86 projects upwardlyfrom the yoke 41 and is received by the slot of the bifurcated lever 83.

In adjusting the instrument, the knob 4 and its shaft 61 are turned andthe small pinion 6'7 drives the large gear wheel 68 through a relativelysmall angle. The pin 71 on the large wheel turns the adjacent lever '72which turns the galvanometer shaft '75 and the lever 83 within thegalvanometer casing. The movements of the lever 83 are then transmittedto the vibrator yoke 41 through the pin and slot connection.

In operation the attendant adjusts the angular position of the vibratorassembly until the surface of the vibrator mirror is parallel to thesurface of the lens in the window. This allows a large beam deflectionfor use with an amplifier as in cardiographology or for other purposeswhere a direct current component is present. As the mirror and magnetunit deflects to overcome the 45 degrees, angular displacement allowed,the vibrator assembly has a full swing in one direction to keep themirror always parallel with the lens surface, or to keep the reflectedspot from the mirror on the photographic surface.

It will be apparent that I have provided a very compact and ruggedgalvanometer which may be immersed in oil without danger of the oilcreeping, which is provided with an adjustable vibrator assembly wherebythe direct current component in the output of an amplifier may becompensated, and which is of improved sensitivity thereby renderingpossible the elimination of one or more stages of amplification andmaking possible a two stage amplifier for cardiograph application.

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that many modifications thereof arepossible. My invention, therefore, is not to be restricted except asnecessitated by the prior art and the scope of the appended claims.

I claim as my invention:

1. In a galvanometer the combination of a vibrator assembly, an oiltight casing, means for pivotally mounting said assembly within thecasing, externally adjustable means extending into the casing forregulating the position of said assembly and a soap packed oil sealbearing for preventing seepage of oil from said casing along saidadjustable means.

2. In combination in a galvanometer, a rectangular plate of non-magneticmaterial having a laterally projecting arm extending from each edgethereof and bent perpendicular to the plane of the plate, magnetizablepole pieces supported by and projecting inwardly to form an air gap between an oppositely disposed pair of said arms, a curved U-shapedmagnetic member arching over and serving as a magnetic return path tosaid air gap and having its ends secured to the outer ends of said polepieces, a vibrator assembly comprising a yoke, and means for pivotallysupporting said yoke between the other pair of projecting arms.

3. In combination in a galvanometer, a rectangular plate having alaterally projecting arm extending from each edge thereof and bentperpendicular to the plane of the plate, magnetizable pole piecessupported by and projecting inward-=- ly to form an air gap between anoppositely disposed pair of said arms, a yoke having bridges thereon, avibrator ribbon, means for tensioning said ribbon between said bridgeson said yoke, an indicating unit comprising a mirror and a permanentmagnet secured to said ribbon, and. means for pivotally supporting saidyoke between the other pair of projecting arms whereby the permanentmagnet on the ribbon is suspended in said air gap.

4. In combination in a galvanometer, a rectangular plate having alateral arm extending from each edge and bent perpendicular to the planeof the plate, a magnetizable structure supported between an oppositelydisposed pair of said arms, indicator means supported between the otherpair of projecting arms in cooperative relation with said magnetizablestructure, an enclosing casing having a window in the front wallthereof, an aperture in said plate, and means for securing said plate tothe inner surface of said front wall with the aperture in alignment withsaid window.

5. In a galvanometer the combination of an oil tight casing, a vibratorassembly, means for pivotally mounting said assembly within said casing,a split bearing in the upper wall of said casing, a shaft extendingthrough said bearing, a flanged shoulder on said shaft, glands in saidbearing, a strong lye soap in said glands, and means for interconnectingthe inner end of said shaft with said vibrator assembly whereby it maybe adjusted by rotating the shaft.

6. In combination in a cardiograph galvanometer a vibrator assemblycomprising a supporting yoke, a vibrator ribbon, bridges on said yokeinclined at an angle to the plane of the yoke, means for tensioning saidribbon over said bridges, indicating means comprising a mirror andpermanent magnet carried by said ribbon, an enclosing casing having awindow, a magnetizable structure, and means for adjustably supportingsaid yoke whereby the position of the mirror relative to the window maybe axially adjusted to compensate for a direct current component in thevariable current.

7. A galvanometer vibrator assembly comprising a supporting yoke, avibrator ribbon, bridges on said yoke having vertical surfaces inclinedat an angle to the plane of the yoke, means for tensioning said ribbonover said surfaces, a pair of magnets secured together on opposite sidesof said ribbon, and a mirror secured to the edges of said pairs ofmagnets.

8. In a galvanometer, a yoke member having a pair of bridges thereon, avibrator ribbon extending between said bridges and means for tensioningit, ribbon-engaging faces on said bridges so formed that the verticalplane defined by said ribbon is angularly relatedto the vertical planeof the yoke member, means for establishing a variable magnetic fieldacross said ribbon in accordance with a quantity to be measured, apermanent magnet secured to said ribbon within said field, means carriedby said ribbon to indicate the deflection thereof under the influence ofvariations in said field, and means for adjustably supporting said yoke.

VERON S. THOMANDER;

